Democrats and Republicans are much less likely to live among each other than they were a generation ago.
Back in 1976 — the year of a close presidential election — just over a quarter of the population lived in "landslide counties," where the winning margin was greater than 20 percentage points, says journalist Bill Bishop, author of The Big Sort: Why the Clustering of Like-Minded America Is Tearing Us Apart.
Last year, more than half the country lived in landslide counties. And, while Barack Obama's margin of victory was less in 2012 than it was in 2008, the number of states decided by fewer than 5 points actually went down.